SHARPSBURG, Md.  Male fish that are growing eggs have been found in the Potomac River near Sharpsburg, a sign that a little-understood type of pollution is spreading downstream from West Virginia, a federal scientist says.

The so-called intersex abnormality may be caused by pollutants from sewage plants, feedlots and factories that can interfere with animals' hormone systems, The Washington Post reported Sunday.

Nine male smallmouth bass taken from the Potomac near Sharpsburg, about 60 miles upstream from Washington, were found to have developed eggs inside their sex organs, said Vicki S. Blazer, a scientist overseeing the research for the U.S. Geological Survey.

Authorities say the problems are likely related to a class of pollutants called endocrine disruptors, which short-circuit animals' natural systems of hormone chemical messages.

Officials are awaiting the results of water-quality testing that might point to a specific chemical behind the fish problems, Blazer said.

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"It certainly indicates something's going on," Blazer said of the new findings in Maryland. "But what, we don't know."

The Potomac River is the main source of drinking water for the Washington metropolitan area and many upstream communities. It provides about 75 percent of the water supply to the 3.6 million residents of Washington and its Maryland and Virginia suburbs.

Blazer, who works at a federal fish lab in Leetown, W.Va., said she found the latest abnormalities last week while examining tissues from fish taken from the river near Sharpsburg.

The same symptoms had previously been found about 170 miles upstream, in the South Branch of the Potomac in Hardy County, W.Va. Blazer and other scientists discovered the problem there last year while investigating a rash of mass fish deaths.

U.S. Fish and Wildlife Service researchers are seeking money for a much larger study across the Potomac watershed.

Endocrine disruptors comprise a vast universe of pollutants capable of driving a hormone system haywire. Some are hormones themselves -- such as human estrogen from women taking birth-control pills or animal hormones washed downstream with manure -- that can pass through sewage plants untouched.

In Hardy County, officials were especially concerned about chicken waste from poultry farms.

Other endocrine disruptors are hormone "mimics" -- industrial chemicals or factory byproducts which confuse the body because they are chemically similar to natural hormones.

These pollutants are often found in very low concentrations, so until recently no equipment could detect them. But the first nationwide survey, in 1999 and 2000, found hormones in about 37 percent of streams tested.

Many scientists are concerned that people, as well as other animals, might be affected. "It's not good news that there's something that feminizes male fish in your water," said Gina Solomon, a senior scientist at the Natural Resources Defense Council.

But the Environmental Protection Agency has not set standards for many of these pollutants. Because of this, many drinking-water plants make no special efforts to remove them.

Authorities in West Virginia are investigating whether there is a link to higher rates of certain cancers in people there.

A recent survey of cancer in Hardy County, where some residents get drinking water from the South Branch, found rates of cancer of the liver, gallbladder, ovaries and uterus that were higher than the state average. All four cancers can in some cases grow faster in the presence of estrogen or chemicals that mimic it, cancer experts said.

"It is at least theoretically possible that those two concepts are worth thinking about side-by-side," said Alan Ducatman, chairman of the Department of Community Medicine at West Virginia University.